" wrote in
:
....
Remember what all the discussions say about keeping the feed line away
from metal objects? Here we are introducing a 5 ft length of metal
just 1/4 inch from the feed line. The extra capacitance just kills the
feed line. Yes, I was using RG-213.

Paul,

The "5 ft length of metal just 1/4 inch from the feed line" is not a good
method of analysing the behaviour.

The treatment of the shield ends is very important to the operation of
these things.

If the shield ends at each end are tied together, and each end
effectively grounded (and that is a big ask), then any common mode
current on the incoming ladder line flows to ground via the outboard
ground connection, and the section of dual coax transforms the impedance
seen looking into the ladder line in a quite predictable way, and with
some loss. The transformed impedance might not be within the range of
your tuner.

If the outboard shield ends are not effectively grounded, then the
configuration does essentially nothing to reduce common mode current
entering the shack, so the system is a fails it its primary objective.

Owen